The behaviour of the narcissist is regulated by a series of routines developed by rote learning and by repetitive patterns of experience. The narcissist finds change extremely distasteful and unsettling. He is a creature of habit. The function of these routines is to reduce his anxiety by transforming a hostile and arbitrary world into a hospitable and manageable one.
Granted, many narcissists are unstable - they often change jobs, apartments, spouses, and vocations. But even these changes are predictable. The narcissistic personality is disorganized - but also rigid. The narcissist finds solace in certainty, in recurrence, in the familiar and the anticipated. It balances his inner precariousness and volatility.
Narcissists often strike their interlocutors as "machine-like", "artificial", "fake", "forced", "insincere", or "spurious". This is because even the narcissist's ostensibly spontaneous behaviours are either planned or automatic. The narcissist is continuously preoccupied with his Narcissistic Supply - how to secure its sources and the next dose. This preoccupation restricts the narcissist's attention span. As a result, he often appears to be aloof, absent-minded, and uninterested in other people, in events around him, and in abstract ideas - unless, of course, they have a direct bearing on his Narcissistic Supply.
The narcissist develops some of his routines to compensate for his inability to attend to his environment. Automatic reactions require much less investment of mental resources (think driving).
(From the book "Malignant Self-love: Narcissism Revisited" by Sam Vaknin - Click on this link to purchase the print book, or 16 e-books, or 2 DVDs with 12 hours of video lectures on narcissists, psychopaths, and abuse in relationships: http://www.narcissistic-abuse.com/thebook.html)